Process for cleaning factory equipment with integrated prerinse

ABSTRACT

A process for cleaning processing equipment for beverages or foods including the steps of 
     (a) pumping a cleaning solution from its holding tank through the processing equipment in the absence of a pre-rinsing step, 
     (b) collecting a first portion of the cleaning solution returning from the processing equipment into a recycling tank, 
     (c) returning to the holding tank for the cleaning solution the main portion of the cleaning solution flowing through the processing equipment, 
     (d) subjecting the first portion of the cleaning solution collected into the recycling tank to a separation process to provide a soil-rich concentrate and a low soil content regenerate, 
     (e) transferring the regenerate to the holding tank for the cleaning solution, and 
     (f) disposing of the soil-rich concentrate as waste.

This is a national stage application of PCT/EP 96/02752 filed Jun. 24,1996.

This is a national stage application of PCT/EP 96/02752 filed Jun. 24,1996 published as WO97/02099 Jan. 23, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a new process sequence for cleaning processingequipment for beverages or foods in the corresponding processing plants.Examples of such processing plants include milk-processing factories,breweries, factories for processing fruit juices and for the manufactureof preserved and deep-frozen foods. The new process affords economic andecological advantages through an integrated recycling step.

2. Discussion of Related Art

The so-called cleaning-in-place (CIP) concept has been successfullyadopted for the cleaning of such plants. This means that the equipmentdesigned to receive and process foods or beverages is provided with itsown installed cleaning system. The cleaning system generally consists ofseveral storage containers for cleaning solution, for prerinse andpost-rinse solutions and optionally for soiled water flowing back. Theindividual cleaning solutions are delivered to the equipment to becleaned through valve-controlled pipes and are optionallypump-circulated up to the end of the cleaning process. The cleaningsolutions themselves may either be strongly acidic or strongly alkaline,i.e. may have pH values of, for example, about 0 to about 2 or in therange from about 12 to about 14. Besides the acids or alkalis, forexample sodium hydroxide, the cleaning solutions optionally containother additives such as, for example, surfactants, defoamers, complexingagents and disinfectants. "Neutral" cleaners with a pH value in therange from about 4 to about 9 are also possible.

In the cleaning-in-place of processing equipment in the food- orbeverage-processing industry, the emptied equipment is normallyprerinsed with water to remove residues of product. The water soiledwith the product residues is normally discharged into the main drainsand is therefore lost to the rest of the process. Accordingly, theprerinse step costs water, time and also energy.

The prerinse step is normally followed by the actual cleaning phase inwhich the cleaning solution is pumped from its holding tank through theequipment to be cleaned and back into the holding tank. The cleaningsolution circulates until the required cleaning effect is achieved. Itbecomes increasingly polluted by the soil removed from the processingequipment and, after a short time, has to be discarded or treated. Inrecent years, regeneration systems such as, for example, Alka Save orNiro Filtration Systems have been brought onto the market for treatingthe soiled cleaning solution. In these regeneration processes, soilcomponents are removed from the cleaning solution so that its usefullife is extended. However, this does not affect the actual cleaningprocess consisting of the prerinse, cleaning and post-rinse steps.

The actual cleaning phase is followed by rinsing with water to removeall traces of the cleaning solution from the processing equipment. Therinsing water accumulating contains residues of the cleaning solutionand soil residues and, to save water, may be used as the prerinsesolution as described in the foregoing. However, the tendency to reusethis water is on the decline for several reasons. There is a danger ofmicroorganisms adapting to the cleaning and disinfecting chemicalspresent in the rinsing water. The germs present in the rinsing solutionand in the corresponding storage tank proliferate and soil componentsaccumulate. Accordingly, germs and soil are additionally introduced intothe equipment to be cleaned in the prerinse step. This adversely affectsthe starting situation for cleaning and disinfection. If an acidiccleaning solution is used, the pH value of the rinsing solution is oftenaround the isoelectric point of the proteinaceous soil to be removed.This makes cleaning very difficult.

The problem addressed by the present invention was to improve thecleaning-in-place process in such a way that the water, time and energydemands would be reduced and, in addition, the soil removed from theprocessing equipment would accumulate in a concentrated form so that itwould be easier to treat or dispose of as waste.

DESCRIPTION OF THE INVENTION

This problem has been solved by a process for cleaning processingequipment for beverages or foods which is characterized in that

a) the cleaning solution is pumped from its holding tank through theprocessing equipment without prerinsing,

b) a first part (=first runnings) of the cleaning solution returningfrom the processing equipment is collected in a recycling tank,

c) the main part of the cleaning solution flowing back after the firstpart is returned to the holding tank for cleaning solution,

d) the first runnings collected in the recycling tank are subjected to aseparation process by which they are separated into a soil-richconcentrate and a low-soil regenerate and

e) the regenerate is transferred to the holding tank for the cleaningsolution and the soil-rich concentrate is disposed of as waste.

In contrast to the existing process, therefore, there is no separateprerinse, the cleaning solution being pumped into the equipment to becleaned without prerinsing in step a). It is advisable to empty theprocessing equipment beforehand. The first part of the cleaning solutionreturning from the processing equipment, referred to herein as the firstrunnings, is still very heavily soiled with product residues from theprocessing equipment. This is reflected in the fact that the cleaningsolution has a greatly increased chemical oxygen demand (COD) throughthe presence of product residues. By contrast, the cleaning solutionreturning after the first runnings has a distinctly reduced COD becauseit is free from the product residues and only contains the detachedsoil.

The core of the invention in its first step consists in separatelycollecting the first runnings soiled with product residues and having anelevated COD value and delivering them to a recycling tank. How much ofthe total volume of the circulating cleaning solution is made up by thefirst runnings in each individual case is specific to the processingequipment to be cleaned and must first be experimentally determined foreach plant by analysis of the COD value. The high-COD first runningscollected in a recycling tank in step b) normally make up about 1 toabout 25% of the total cleaning solution used.

The main part of the cleaning solution flowing back after the firstrunnings is delivered to the holding tank for the cleaning solution andis optionally circulated until the required cleaning effect is achieved.

Step d) is the second step crucial to the invention. In this step, theproduct-soiled high-COD first runnings collected in the recycling tankare subjected to a separation process. In this separation process, thefirst runnings are separated into a soil-rich concentrate and a low-soilregenerate which still has largely the acid or alkali content of thecleaning solution. The separation process used is preferably a membraneprocess and, more particularly, microfiltration, ultrafiltration ornanofiltration. Nanofiltration is particularly preferred. In the case ofthe widely used alkaline cleaning solutions, a ceramic membrane or analkali-stable organic polymer membrane (for example of the type marketedby Membrane Products Kyriat Weizmann of Rehovot, Israel) may be used forthe nanofiltration process.

The extent to which the first runnings collected in the recycling tankcan be separated by such a membrane process into a reusable regenerate(permeate) and a retentate for disposal as waste will depend on thenature and degree of soiling by food or beverage residues. Inexperimental laboratory tests with artificially prepared soiled firstrunnings using such beverages as, for example, milk or beer, it wasfound that around 60 to 95% by volume of the first runnings could berecovered as regenerate under simulated practical conditions. Theprocess as a whole is more economical, the larger the amount ofregenerate obtainable.

The regenerate, which still largely contains the acid in the case ofacidic cleaning solutions and the alkalinity in the case of alkalinecleaning solutions, is transferred to the holding tank for the cleaningsolution. However, since part of the acid or alkalinity is lost throughchemical consumption or retention in the retentate and since, inaddition, additives such as, for example, surfactants or defoamers areretained in the retentate, the active chemicals consumed or removed haveto be periodically replaced. The simplest way of doing this is to usethe electrical conductivity of the cleaning solution as the controlparameter for replacement and automatically to introduce anactive-substance concentrate from a storage container whenever theconcentration level falls below a preset minimum value.

The soil-rich concentrate, which may have a solids content of about 25to 35% by weight, is preferably disposed of separately, for example byburning or by biological degradation, for example in a digesting tower.The concentrate could of course also be added to the normal processwastewater although this is less preferable for ecological reasons.

There is generally no need to adjust the temperature of thesoil-containing cleaning solution collected in the recycling tank to acertain value for the separation process. Instead, the temperaturemaintained in the cleaning circuit of the particular processingequipment may be retained. In the case of milk-processing equipment,this temperature is normally well above room temperature and may be, forexample, in the range from about 50° to about 80° C.; in the cleaning ofmilk heaters, it may even exceed 90° C. By contrast, in the cleaning ofbrewing equipment, temperatures around room temperature are sufficient.In order to avoid additional energy consumption, the first runningscollected in the recycling tank are subjected to the separation processat their particular temperature.

Even though the cleaning solution is largely regenerated by theabove-described process, a very small percentage by volume is dischargedas soil-containing retentate. The resulting loss is preferably made upduring the next step of the cleaning process as a whole. After theactual cleaning phase and the return of the cleaning solution to itsholding tank, the processing equipment is rinsed with fresh water toflush out residues of the cleaning solution. The first part of therinsing water returning from the processing equipment thus contains themain part of the cleaning solution remaining in the processingequipment. Now, such a large percentage of the first rinsing waterflowing back is returned to the holding tank for cleaning solution thatthe proportion by volume lost through removal of the soil is replaced.Since this first part of the rinsing water still contains activeingredients of the cleaning solution, this procedure is more economicalthan replacing the lost volume with fresh cleaning solution.

Accordingly, the process according to the invention has the followingadvantages over existing processes:

There is no need for separate prerinsing of the processing equipment sothat no rinsing water for disposal accumulates and, in addition, timeand energy are saved.

Only a small proportion of the actual cleaning solution ("firstrunnings") is subjected to a separation process so that the separationunit can have relatively small dimensions and can be operated with areduced energy consumption than if the entire cleaning solution were tobe regenerated. The first part of the rinsing water containing residuesof the cleaning solution is added to the cleaning solution so that theactive substances can be reused. The rest of the rinsing water is onlylightly soiled and may safely be discharged into the main drains or, ifdesired, may even be further treated.

There is no need to store the rinsing water for subsequent use as aprerinse solution so that there is no danger of microorganismsaccumulating and adapting to the active ingredients.

Wastewater pollution is distinctly reduced by the direct disposal of theheavily soil-laden retentate from the separation of the first runnings,for example by burning or digestion in a digestion tower.

In addition, the danger of microbiological contamination is reduced inrelation to the conventional process where the post-rinse solution isused for prerinsing in the next step. Compared with earlier processeswhich directly use fresh water for prerinsing the processing equipment,the process according to the invention leads to complete saving of theprerinsing water.

The useful life of the cleaning solution can be lengthened if, duringprolonged stoppages, for example at weekends, the entire cleaningsolution is subjected to the separation process of which the capacityduring normal working hours only has to suffice to separate the firstrunnings.

Separation step d) is explained by way of example in the following:

The effect of nanofiltration on simulated first runnings of cleaningsolutions was investigated in laboratory tests. A commerciallyobtainable nanofiltration membrane based on organic polymers (supplier:Membrane Products Kyriat Weizmann, Rehovot, Israel) was used for thispurpose.

In a first test, first runnings from the cleaning of a milk heater weresimulated. To this end, 11.6 kg of whole-milk powder (26% by weight fatin dry matter) and 3 kg of 50% by weight sodium hydroxide were made upwith water to 100 kg. The resulting solution was saponified withstirring for 4 hours at 65° C. and then diluted with water in a ratio byvolume of 1:1. The hydroxide content was then determined by titrationand adjusted to an Na(OH) content of 1.5% by weight by addition ofsodium hydroxide.

The solution was filtered through the nanofiltration membrane at atemperature of 60° C. Over the first 25 hours, the membrane flow fellfrom 22 liters per hour per square meter (L/hm²) to 10 L/hm² while theCOD of the retentate increased from 80,000 to 150,000; the permeate hada COD of 10,000 after 25 hours. Fresh solution was added on theretentate side so that the COD of the retentate decreased and membraneflow increased. The test was continued for another 150 hours, freshsolution being added on the retentate side four times after an intervalof 25 hours. After a total running time of 175 hours, the COD of theretentate had increased to 380,000. The COD of the permeate was 50,000.

In a second test, 5 kg of water and 840 g of 50% by weight sodiumhydroxide were added to 2.5 kg of whole milk (fat content 3.5% byweight), followed by stirring for 4 hours at 80° C. The solution wasmade up to 40 liters with water. 200 g of disodium ethylenediaminetetraacetate were then added. The solution had a COD of 10,000. It waspassed through the nanofiltration membrane with a temperature of 50° to65° C.

For a temperature of 50° C. at the beginning of the filtration process,the membrane flow amounted to 30 L/hm² ; the permeate had a COD value ofabout 300. Over the first ten hours' filtration, the temperature of thesolution was increased to 65° C. The membrane flow increased to 40L/hm². The temperature was lowered to 60° C. and kept at that level forthe remainder of the test. Over a total filtration time of 70 hours, theCOD of the retentate increased to 30,000. The COD of the permeate was1,000. On termination of the test, the membrane flow was 25 L/hm².

What is claimed is:
 1. The process of cleaning processing equipment forbeverages and foods consisting essentially of:(a) pumping a cleaningsolution from its holding tank through said processing equipment in theabsence of a pre-rinsing step; (b) collecting a first portion of saidcleaning solution returning from said processing equipment into arecycling tank; (c) returning to the holding tank for said cleaningsolution the main portion of the cleaning solution flowing through saidprocessing equipment; (d) subjecting said first portion of said cleaningsolution collected into said recycling tank to a separation process toprovide a soil-rich concentrate and a low soil content regenerate; (e)transferring said regenerate to the holding tank for said cleaningsolution; (f) disposing of said soil-rich concentrate as waste; and (g)rinsing said processing equipment with fresh water and delivering therinse water to the holding tank for said cleaning solution to replacethe volume of soil-rich concentrate removed in (d) and (f).
 2. A processas in claim 1 wherein said first portion of said cleaning solutioncollected in step (b) comprises about 1% to 25% by volume of the totalcleaning solution employed in the process.
 3. A process as in claim 1wherein said separation process in step (d) comprises a membraneseparation process.
 4. A process as in claim 3 wherein said membraneseparation process is conducted by microfiltration, ultrafiltration, ornanofiltration.
 5. A process as in claim 1 wherein said separationprocess in step (d) is continued until 60% to 95% by volume of saidfirst portion of said cleaning solution has been obtained as a low soilcontent regenerate.